FIG. 6 is a schematic sectional view taken along a shaft center of a drive mechanism of a wind turbine. In FIG. 6, a plurality of blades (normally three to five blades) are rotatably mounted on a rotor head 3 via a bearing 2. The rotation of the blades 1 are transmitted to the rotor head 3. A first inner ring 5 is connected to the rotor head 4 via a plurality of bolts 4. The rotation of the rotor head 3 is transmitted to the first inner ring 5 via the bolts 4.
The gear coupling 07 is configured by meshing simultaneously the outer ring 7 with the internal teeth, the first inner ring 5 with the external teeth meshing with the internal teeth of the outer ring 7, and a second inner ring formed with external teeth. The outer ring 7 is not fixed to any of the parts but is prevented from coming out in the axial direction of the outer ring 7 by means of the rotor head 3 and a cover plate 20. The cover plate 20 is described in detail later.
A bearing sleeve 8 fixed to an outer circumferential part of the rotor head 3 is supported in a casing 15 via a main bearing 9. The casing 15 is supported on a tower via a bearing 17.
In the gear coupling 07, the external teeth of the first inner ring 5 and the internal teeth of the outer ring 7 mesh with each other and the internal teeth of the outer ring 7 and the external teeth of the second inner ring 6 mesh with each other so as to transmit the rotation to the drive shaft 10 via a plurality of bolts 16 while the second inner ring 6 functions as an output end. In this manner, the rotation of the rotor head 3 is transmitted to the drive shaft 10 via the gear coupling 07 and thus, the gear coupling 07 can absorb axial misalignment of the rotor head 3 and the drive shaft 10 and the movement of the rotor head 3 and the drive shaft 10 in the axial direction due to thermal expansion difference caused by temperature difference between the rotor head 3 and the drive shaft 10 as well as the vibration transmitted to the drive shaft 10 from the rotor head 3.
The rotation of the drive shaft 10 is transmitted to a step-up gear 11 to increase the speed by a prescribed ratio, thereby driving a generator 13.
An interior space 12 is formed inside the gear coupling 07 (12s is a cover/a sealing member). An exterior space 19 is formed outside of the outer ring 7. The lubricant such as grease, oil or the like is housed in the interior space 12 and the exterior space 19.
FIG. 7 shows an exemplary case of a conventional sealing member for a lubricant storage part 19s consisting of the interior space 12 and the exterior space 19.
In FIG. 7, a cloth-inserted rubber sheet 21 is made of cloth and rubber. The cover plate 20 on the side of the bearing sleeve 8 is fixed to the bearing sleeve 8 by a plurality of bolts (unshown). One end of the cloth-inserted rubber sheet 21 is fixed to the cover plate 20 on an inner circumferential side thereof via a stopper plate 23 and a rubber member 22 by a bolt. The cloth-inserted rubber sheet 21 is bent at a right angle and its other end is fixed to a top surface of the drive shaft 10 via a rubber member 22a. 
The other end of the of the cloth-inserted rubber sheet 21 is firmly fixed to the top surface of the drive shaft 10 by applying contact pressure by means of an iron band 41. The iron band is retained by fixing a retaining plate by a bolt 25.
In this manner, leaking of the lubricant such as grease and oil is prevented in the interior space 12 formed inside of the gear coupling 07 and the exterior space 19s of the outer ring 7.
Patent Document 1 (JP5-88701 Utility Model) discloses a device for preventing the lubricant of the gear coupling from leaking.
Patent Document 2 (JP7-14226 Utility Model) proposes to prevent compression set and leaking of the lubricant due to compressibility fluctuation of an O-ring of the gear coupling.
[PATENT DOCUMENT 1] JP5-88701U (Published Utility Model Application)
[PATENT DOCUMENT 2] JP7-14226U (Published Utility Model Application)